With the increasing dependence of an enterprise on information access, the influences of a data center on the daily business of the enterprise are also increasing. Once a fault occurs to the data center in the enterprise, the normal operation of the enterprise's daily business will be greatly impacted, causing significant losses to the enterprise. Generally speaking, when a fault occurs to the data center, the losses suffered by the enterprise fall into the following categories: impact on the daily enterprise work (e.g. employees cannot work as normal), direct property loss (e.g. loss of orders, compensation to the loss of the enterprise's partners, etc.), damages to the enterprise's reputation (e.g. loss of some clients). Therefore, the reliability has become an important aspect in evaluating the quality of a data center.